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Encode QRCode in .NET Note

The second line of this code reads the first line of text from the file, meaning the file pointer is waiting at the start of the second line of data. However, the following f.puts statement then puts a new line of text into the file at that position. Unfortunately, this action will not push the previously existing second line to the third line of the file. All it does is overwrite the equivalent number of bytes, so you end up with a broken third line! This behavior means you really need to think carefully before writing data into the middle of an existing file, as you may not get the outcome you thought you would! Whereas puts outputs lines of text, you can perform the writing equivalents of getc and read with putc and write: f = File.open("text.txt", "r+") f.putc "X" f.close This example opens text.txt for reading and writing, and changes the first character of the first line to X. Similarly: f = File.open("text.txt", "r+") f.write "123456" f.close This example overwrites the first six characters of the first line with 123456.

The first step in using any custom control in ASP.NET is the @ Register directive, as shown here: <%@ Register TagPrefix="06" TagName="login" Src="Login.ascx" %> In this example, the TagP refix attribute specifies the prefix to be used within the tag that will place the control on the page. The TagName attribute specifies the name of the control. Taken together, these attributes mean that to create an instance of the control in the .aspx file, we need to use the tag <06:login />. Note Although you might presume that ASP.NET would know that <06:login> is a user control and thus a server control that should be run on the server, you d be incorrect. If you don t include a RunAt=Server attribute/value pair inside the <06:login> tag, the tag will be sent back to the client browser unaltered. The Src attribute points to the location of the .ascx file. This location is relative to the current directory, so in this example, we don t precede the name with any path qualifier. Note One magical character can be used when declaring source paths in ASP.NET. The tilde (~) character starts the path at the root of the application, similar to the way the slash (/) character starts the path at the root of the site. This shortcut seems less useful than it really is, and you might think you don t need it, but wait until you work with Web applications that have many directories. An alternative form of the @ Register directive allows you to register a component when all you have is the DLL created from the source. This alternative is commonly used for controls created entirely in code. The format of the directive is shown here:

The DbDataAdapter object is used to retrieve and update data between a DataTable and a data store (such as a SQL Server database). The DbDataAdapter is derived from the DataAdapter class and is the base class of the provider-specific DbDataAdapter classes. Provider-specific versions of DbDataAdapter are created for each type of provider, such as SQL Server, Oracle, and XML. The DbDataAdapter class has the SelectCommand property that you use to define how data is to be retrieved. The SelectCommand must contain a valid DbCommand object, which must have a valid connection. You can also use DbDataAdapter to update changes to the data source. You ll learn more about this in the next section.) The DataAdapter.Fill method moves data from the data store to the DataTable object that you pass into this method. The Fill method has several overloads, some of which accept only a DataSet as a parameter. When a DataSet is passed to the Fill method, a new DataTable object is created in the DataSet if a source DataTable object is not specified. The following code uses the System.Configuration.ConfigurationManager to read the connection string from a Web.config file. It then uses System.Data.Common.DbConnection to represent a database connection. It also uses System.Data.SqlClient to work directly with a SQL Server database. Finally, it shows how you can use the DataAdapter.Fill method to load a DataTable directly from a SQL Server database.

4. You oversee administration for a wide area network (WAN) belonging to the Proseware company, which has one central office in Rochester and two branch offices in Buffalo and Syracuse. The network, which consists of one domain, has one primary DNS zone running on a Windows Server 2003 computer at the central office, and one secondary DNS zone at each branch. Network users are complain ing that they often cannot connect to sites at remote branches. Administrators have determined that network bandwidth between the central office and branches has become saturated with zone transfers, and that zone transfers are being initiated before they can complete. Which of the following steps would help resolve the problem with the least effort a. Install Active Directory on the network, and promote the servers hosting the secondary DNS zones to domain controllers. b. Increase the network bandwidth by establishing a fiber-optic connection between the two sites. c. Increase the refresh interval on the primary DNS server. d. Increase the refresh interval on the secondary DNS servers. 5. You discover that an administrator has adjusted the default TTL value for your company s primary DNS zone to 5 minutes. Which of the following is the most likely effect of this change a. Resource records cached on the primary DNS server expire after 5 minutes. b. DNS clients have to query the server more frequently to resolve names for which the server is authoritative. c. Secondary servers initiate a zone transfer every 5 minutes. d. DNS hosts reregister their records more frequently.

The System.Collections.Specialized namespace also contains the CollectionUtil class, which we think would be better located in the main System.Collections namespace. Static methods of this factory class create case-insensitive instances of the ArrayList and Hashtable classes discussed earlier. This is achieved by using case-insensitive implementations of the underlying hash code provider and comparer.